/Engine/Source/Editor/UnrealEd/Public/EditorWorldExtension.h
List of extensions along with their reference count. Extensions will only be truly removed and Shutdown() after their reference count drops to zero.
typedef [TTuple](API\Runtime\Core\Misc\TTuple)< [UEditorWorldExtension](API\Editor\UnrealEd\UEditorWorldExtension) *, int32 > FEditorExtensionTuple